Compressed gas cylinder cabinet with regulated exhaust control

ABSTRACT

A gas cabinet and a method of controlling air flow through said gas cabinet. The gas cabinet includes an enclosure; a damper having at least two flow rate positions; an exhaust outlet; a set of sensors; and a programmable logic controller configured to change a flow rate position of the damper from a first flow rate position to a second flow rate position based on the state of the sensors. The method includes using the damper to lower the amount of exhausted air required under normal operating conditions and using the damper to increase the amount of exhausted air when a possible gas leak is detected.

FIELD OF THE INVENTION

The present invention relates to the field of industrial gas supplysystems; more specifically, it relates to a compressed gas cylindercabinet with regulated exhaust control and a method of regulatingexhaust of a compressed gas cylinder cabinet.

BACKGROUND

The extensive use of compressed and highly toxic gases in thefabrication of electronic semiconductor devices has led to the use ofgas cabinets for containment of the compressed gas cylinders. In orderto protect personnel in the case of a toxic gas leak from a cylinder inthe cabinet, the cabinets are exhausted. Typically, a gas cabinet willexhaust several hundred cubic feet per minute of temperature andhumidity conditioned air at all times. Because of the amount of energyrequired to condition the air and run the exhaust fans continuously, thecost in energy consumption is very high. Accordingly, there exists aneed in the art to mitigate the deficiencies and limitations describedhereinabove.

SUMMARY

A first aspect of the present invention is a gas cabinet, comprising: anenclosure; a damper having at least two flow rate positions; an exhaustoutlet; a set of sensors; and a programmable logic controller configuredto change a flow rate position of the damper from a first flow rateposition to a second flow rate position based on the state of thesensors.

A second aspect of the present invention is a method, comprising:providing a gas cabinet, comprising: an enclosure; a damper having atleast two flow rate positions; an exhaust outlet; a set of sensors; anda programmable logic controller configured to change the flow rateposition of the damper from a first flow rate position to a second flowrate position based on the state of the sensors; and if the exhauststatic pressure within the cabinet is lower than a preset minimumpressure then changing the damper from the first flow rate position tothe second flow rate position if one or more sensors of the set ofsensors indicates a gas leak within the enclosure, the second flow rateposition having a higher flow rate than the first flow rate position.

These and other aspects of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a compressed gas cabinet according to theembodiments of present invention;

FIG. 2 is a schematic diagram of an exhaust system for the compressedgas cabinet of FIG. 1;

FIG. 3A is a front view, FIG. 3B is a sectional view through line 3B-3Bof FIG. 3A, and FIG. 3C is a top view of the damper assembly of FIG. 1;

FIGS. 4A, 4B and 4C illustrate various positions of the damper of FIG.1.

FIG. 5 is a top view of a first alternative damper assembly according toembodiments of the present invention;

FIG. 6 is a front view of a second alternative damper assembly accordingto embodiments of the present invention;

FIG. 7 is a side view of a third alternative damper assembly accordingto embodiments of the present invention;

FIG. 8 is a schematic diagram of a control system for the compressed gascabinet of FIG. 1;

FIGS. 9A, 9B and 9C are flowcharts illustrating the logic of theprogrammable logic controller of FIG. 8; and

FIG. 10 is a schematic block diagram of an exemplary programmable logiccontroller.

DETAILED DESCRIPTION

The embodiments of the present invention include a compressed gascylinder cabinet that includes an array of sensors and a programmablelogic controller (PLC) that automatically controls the quantity of airflow drawn into the cabinet based on the sensor data using anelectromechanical damper to increase or decrease the flow of air intothe cabinet and the speed of the exhaust fan and thus the amount of airflowing into the cabinet and ultimately exhausted from the cabinet. Thedamper will be controlled by the PLC, wherein exhaust requirements aredetermined. The exhaust requirements are determined by sensors insidethe cabinet, a gas detector in the cabinet and sensors in the exhaustducting. Reducing the need for continuously high flow amounts of airthrough the cabinet increases the sensitivity of the gas detector. Thesensors measure gas delivery pressure, gas cylinder pressure, gas flow,exhaust velocity, exhaust static pressure, cylinder weight and whetherthe gas cabinet is in normal or maintenance mode.

Under normal operating conditions, the damper will be closed and thecabinet interior will be held at a pressure that is negative to thecabinet exterior so there will be none to very little air flow andattendant waste of energy. The PLC will monitor several sensors andautomatically open the damper to provide necessary exhaust flow whenneeded. The PLC monitors for a possible gas leak in the cabinet and if arequest for access to the interior of the cabinet has been initiated.The parameters of the exhaust flow determination logic are configuredbased on cylinder pressures, gas delivery pressures, gas flow rates andgas hazard classification. Each sensor has a programmable set point andacceptable range that the PLC uses to determine the damper setting.

The damper setting is based on, for example, one or more of (1)detection of the gas inside the cabinet; (2) is the air pressure insidethe cabinet negative relative to the to air pressure outside the cabinetwithin a specified range; (3) is the gas flow within a specified range;(4) is the gas cylinder pressure within a specified range; (5) is thegas delivery pressure within a specified range; (6) have there beendynamic changes in gas cylinder pressure or delivery pressure; (7) havethere been dynamic changes in gas cylinder weight; (8) is there a needfor personnel to access the interior of the cabinet; and (9) when thedamper is open, is the exhaust pressure within a specified range. Adynamic change is defined in a time rate of change in the parameter thatexceeds the time rate of change of that parameter under normal gas usagewhich is programmed into the PLC.

FIG. 1 is an isometric view of a compressed gas cabinet according to theembodiments of present invention. In FIG. 1, a compressed gas cabinet100 for holding a compressed gas cylinder 105 includes an exhaust duct110 open to the interior of the cabinet, a fixed left side 115A, a fixedright side 115B, a fixed top 120, a fixed bottom 125, a fixed back wall130 and a cabinet door 135 attached to left side 115A by a hinge 140. Itis preferred that exhaust duct 110, sides 115A and 115B, top 120, bottom125 and back 130 be joined in an airtight manner. Door 135 includes adamper 145 which comprises an array of openings 150 and a positionalactuator 155. Door 135 also includes a window 160 connected to the doorby a hinge 165 and including a window open/closed sensor 170. Window 170is fitted with a latch (not shown) on the outside of the door. In oneexample, window 160 is sealed air-tight in the closed and latchedposition. Door 135 is also fitted with a door latch 175. In one example,door 135 is sealed air-tight in the closed and latched position. Thewindow and door latch 175 are under the control of the PLC but may befitted with manual overrides.

Right side 115A includes a door open/closed sensor 180 and is penetratedby a purge line 185. Purge line 185 is sealed air-tight to sidewall115B. Top 120 is penetrated by a gas supply line 190 in order to supplygas from gas cylinder 105 to a fabrication line tool (e.g., plasma etchor deposition tool, chemical vapor deposition tool. etc.) not shown. Gassupply line 190 is sealed air-tight to top 120. In one example, thereare no openings in sides 115A and 115B, top 120, bottom 125 and back 130that allow outside air to enter cabinet 100. A gas sensor 195 is fittedto exhaust duct 110 so as to be able to detect the presence of gas fromcylinder 105 in the exhaust stream. Alternatively, gas sensor 195 may bemounted inside cabinet 100.

Cabinet 100 includes a cylinder weight sensor 200 (e.g., a scale) uponwhich gas cylinder 105 sits and a strap 205 for securing the gascylinder to back wall 130 of the cabinet. Cabinet 100 further includes apneumatic cylinder valve 210, a gas flow sensor 215 (e.g., a mass flowmeter), a high pressure sensor 220, a high pressure isolation valve 225,a gas pressure regulator 230, a low pressure sensor 235, a low pressureisolation valve 240, a purge valve 245 and a vent valve 250. Pneumaticcylinder valve 210 allows connection of gas cylinder 105 to the gasdelivery and vent lines inside cabinet 100. Gas flow sensor 215 measuresthe rate of gas flow from cylinder 105 to the gas delivery lines. Highpressure sensor 220 monitors the pressure within the cylinder whenpneumatic cylinder valve 210 is open. High pressure isolation valve 225controls gas flow to pressure regulator 230 (which lowers the pressureof the gas supplied to the tool). Pressure regulator 230 sets the toolsupply gas pressure and low pressure sensor 235 monitors the gaspressure supplied to the tool. Low pressure isolation valve 240 isolatesthe gas delivery and vent lines from the tool. Purge valve 245 and ventvalve 250 allow purging and venting of toxic gas to exhaust duct 110.

Pneumatic cylinder valve 210, high pressure isolation valve 225, gaspressure regulator 230, low pressure isolation valve 240, purge valve245 and vent valve 250 may be manually operated when the cabinet door135 or access window 160 is open or remotely operated when the accessdoor and/or window is closed or open. Door latch 175 and the windowlatch (not shown) are normally unlatched remotely, but may include amanual (e.g., key) override. With cabinet door 135, window 160 anddamper 145 closed, gas cabinet 100 is hermetically sealed.

FIG. 2 is a schematic diagram of an exhaust system for the compressedgas cabinet of FIG. 1. In FIG. 2, an exhaust plenum 255 is connected toexhaust duct 110 of gas cabinet 100. Two exhaust fans 260A and 260Bhaving motors 265A and 265B are connected to exhaust plenum 255 by ducts270A and 270B respectively. Motors 265A and 265B are controlled byvariable frequency drive (VFD) controls 275A and 275B respectively.Contained within cabinet 100 (or alternatively, within exhaust duct 110)is an exhaust static pressure sensor 280 which indicates the pressurewithin the cabinet or exhaust duct relative to the pressure outside ofthe cabinet. Contained within exhaust plenum 255 is an exhaust flowsensor 285 which measures the cubic feet per minute (CFM) being drawn byfans 260A and 260B. While two exhaust fans are illustrated forredundancy and added safety, a single fan may be used.

FIG. 3A is a front view, FIG. 3B is a sectional view through line 3B-3Bof FIG. 3A, and FIG. 3C is a top view of the damper assembly of FIG. 1.In FIG. 3A a grate 290 having openings 295 is positioned over openings150 of door 135 and held moveably in position by a frame 300. Positionalactuator 155 is connected to grate 290 by an actuator arm 292. In theexample of FIG. 3A and 3B, openings 295 circular are larger in diameterthan openings 150 which are also circular. It should be understood, thatopenings 150 and 295 may have shapes other than circular (e.g., square,rectangular, oval, or polygonal) and that openings 150 may be largerthan openings 295 as long as grate 290 can completely block openings 150in the fully closed position. Actuator 155 may be configured to movegrate 290 between first and second positions, so damper 145 is fullyopen (see FIG. 4A), or fully closed (see FIG. 4C) or configured to movegrate 290 in any position (see FIG. 4B) between the first and secondposition so the damper may be fully open, partially open, partiallyclosed or fully closed. The default (e.g., no power) position of damper145 is fully closed. While actuator 155 has an internal spring and gearassembly that would close grate 290 in the event of a power failure, anoptional spring 307 (or other closing assist means) is provided. In FIG.3C, seals/slides 305 are fitted between grate 290 and door 135 and frame300.

FIGS. 4A, 4B and 4C illustrate various positions of the damper ofFIG. 1. In FIG. 4A, grate 290 is in the fully open position (i.e., grate290 does not block any regions of openings 150). In FIG. 4B, grate 290is in a partially open (or closed) position (i.e., grate 290 blocksregions of openings 150). In FIG. 4C, grate 290 is in the fully closedposition (i.e., grate 290 blocks all regions of openings 150). In thefully closed position, negative pressure (relative to the ambientpressure outside of the cabinet) inside cabinet 100 compresses grate 290against cabinet door 135 to seal the damper. In one example, a normaloperating position of damper 145 is fully closed position to totallystop air flow into the gas cabinet or a partially opened position so asto reduce the air flow to about 10% or less of the air flow into the gascabinet when damper 145 is in the fully opened position. In one example,an emergency position of damper 145 is a fully open position. In oneexample, a maintenance position of damper 145 is a partially openposition, which is more opened than the normal operating position butnot completely open. In one example, a maintenance position of damper145 is the fully open position. For example, given a maximum flow ofabout 300 CFM with the damper in the fully open position, the flow inthe normal operating position is between about 0 CFM and about 10 CFMand in the maintenance position s between about 150 CFM and about 250CFM. These CFM values are converted into grate positions and areadjustable and programmable.

FIG. 5 is a top view of a first alternative damper assembly according toembodiments of the present invention. In FIG. 5, a damper 145A includesa grate 290A (similar to grate 290 of FIG. 3C) that is held in placeover a single large opening in door 135 by a frame 300A. Positionalactuator 155 (see FIG. 1) connected to grate 290A by actuator arm 292A.A region 308 of frame 300A includes an array of openings (not shown)similar to openings 150 of FIGS. 3A and 3B. Positional actuator 155 (seeFIG. 1) is connected grate 290A. Damper assembly 145A is mounted to theoutside of door 135. Operation of damper 145A is similar to damper 145of FIGS. 4A, 4B and 4C.

FIG. 6 is a front view of a second alternative damper assembly accordingto embodiments of the present invention. In FIG. 6, a damper assembly145B includes a set of wedge shape openings 310 in door 135 and arotatable plate 315 having wedge shaped openings 320. Openings 310 indoor 135 are arranged in a ring array about a center 325. Openings 320in plate 315 are also arranged in a ring array about center 325. Plate315 is rotatable about center 325 by means of an actuator arm 292Boffset horizontally from center 325. Actuator arm is connected topositional actuator 155 (see FIG. 1) and is configured to rotate plate315 to completely block, partially block or not block openings 310.Damper assembly 145B is illustrated in the fully open position. Damperassembly 145B is mounted to the outside of door 135. The default (e.g.,no power) position of damper 145B is fully closed. An optional spring307B (or other closing assist means) assists closing damper 145B in theevent of a power failure. Seals (not shown) may be provided betweenplate 320 and door 135. While illustrated as integral with door 135, adamper assembly incorporating openings 310 in a second plate may befabricated for placement in a single large opening in door 135.Operation of damper 145B as to normal, maintenance and emergency CFMflow is similar to damper 145 of FIG. 3A. Optionally, an off centerweight may be attached to plate 315 to assist in closing damper 145B.

FIG. 7 is a side view of a third alternative damper assembly accordingto embodiments of the present invention. In FIG. 7, a damper assembly145C comprises louvers 330 mounted on a frame 335 which is mounted todoor 135 over an opening 340 in door 135. Positional actuator 155 (seeFIG. 1) connected to louvers 330 by actuator arm 292C and may be adaptedto completely open louvers 330, partially close louvers 330 orcompletely close louvers 330 thereby blocking openings 340. Damperassembly 145C is illustrated in the full open position. An optionalspring 307C (or other closing assist means) assists closing damper 145Bin the event of a power failure. Seals (not shown) may be providesbetween adjacent louvers 330 and between louvers 330 and door 135.Optionally, a weight may be attached to plate the lower end of to assistin closing damper 145B. Operation of damper 145C as to normal,maintenance and emergency CFM flow is similar to damper 145 of FIG. 3A.

FIG. 8 is a schematic diagram of a control system for the compressed gascabinet of FIG. 1. In FIG. 8, a PLC 345 is connected to receive inputfrom door open sensor 180, window open sensor 170, high pressure sensor220, low pressure sensor 235, cylinder weight sensor 200, gas sensor195, flow sensor 215, exhaust static pressure sensor 280 and exhaustflow sensor 285. PLC 345 is connected to send control signals to cabinetdoor latch 175, pneumatic cylinder valve 210, low pressure isolationvalve 235 and high pressure isolation valve 225. PLC 345 is connected toreceive from and send signals to VFD 275. PLC 345 may include humaninterface devices such as a display, keyboard, and means for enteringdata (e.g., parameter set points and control ranges) into andprogramming the logic of the PLC. In one example, PLC 345 may comprise ageneral-purpose computer.

FIGS. 9A, 9B and 9C are flow charts illustrating the logic of PLC 345 ofFIG. 8. FIG. 9A describes the control logic for normal/emergencyoperation of the gas cabinet. In step 400, PLC 345 of FIG. 8 isinitialized by loading a control program (which sets up a state machine)and entering parameter set points specified control ranges for thevarious sensors into memory or resetting the logic state machinepreviously defined by the control program. In step 405, the damper(e.g., damper 145 of FIG. 3) is set to the normal operating position bycontrol signals sent to the actuator (e.g., actuator 155 of FIG. 3) andexhaust fans 260A and 260B of FIG. 2 are ramped up to the correspondingpressure and flow rate for the normal operating position of the damperby control signals sent by PLC 345 to VFDs 275 of FIG. 2. In step 410,gas flow sensor 215, gas sensor 195, cylinder weight sensor 200, lowpressure sensor 235, high pressure sensor 220 of FIGS. 1 and 8 aremonitored, checking if each sensor is reading within the specifiedcontrol range. In step 415, the sensors are polled to determine if afault has been detected. If a fault is detected then step 420 isperformed, else the loop of step 410 and 415 is repeated.

The sensors polled are:

(1) gas flow sensor 215 of FIGS. 1 and 8 to determine if the gas flowexceeds a specified value in case the PLC generates a gas flow faultsignal;

(2) low pressure sensor 235 of FIGS. 1 and 8 to determine if a dynamicchange in gas pressure over a specified amount of time exceeds aspecified value in which case the PLC generates a low pressure faultsignal;

(3) cylinder weight sensor 200 of FIGS. 1 and 8 to determine if therehas been dynamic change in cylinder weight over a specified amount oftime exceeds a specified value (which could indicate a gas leak) inwhich case the PLC generates a cylinder weight fault;

(4) high pressure sensor 220 of FIGS. 1 and 8 to determine if a dynamicchange in gas pressure over a specified amount of time exceeds aspecified value in which case the PLC generates a high pressure faultsignal; and

(5) gas sensor 195 of FIGS. 1 and 8 to determine if gas has beendetected in the exhaust stack in which case the PLC generates a gas leakfault signal.

In step 420, the fault type is displayed (if the PLC is so equipped) andexhaust fans 260A and 260B of FIG. 2 are ramped up to a fan speed thatcorresponds to a preset exhaust pressure and exhaust flow rate for theemergency (e.g. an open) damper position. Note the damper is not yet inthe emergency position. This is accomplished by control signals sent byPLC 345 to VFDs 275 of FIG. 2. The fault type may also be indicated bycolored lights and/or audible tones. The fault type may be networked toremote monitoring stations. Note, the PLC itself may be remote from thegas cabinet and connected to a network interface that is connected tothe various sensors and control valves of the gas cabinet and alsoconnected an additional network interface connected to the VFDs andexhaust sensors. Additionally, high pressure isolation valve 225, lowpressure valve isolation valve 240, and pneumatic cylinder valve 210 ofFIGS. 1 and 8 are closed by a control signals sent by PLC 345 to thosevalves. Next, in step 425, exhaust static pressure sensor 280 of FIGS. 2and 8 is polled to determine if the pressure is lower than a specifiedmaximum pressure. This is a check that the cabinet is at a negativepressure compared to the ambient air pressure outside the cabinet. Ifthe pressure is above the maximum pressure then in step 430, PLC 345initiates an exhaust pressure alarm and no further action is takenautomatically. If in step 425, the pressure is lower than the specifiedmaximum pressure, step 435 is performed. In step 435, the damper (e.g.,damper 145 of FIG.3) is set to the emergency position by control signalssent to the actuator (e.g., actuator 155 of FIG. 3) and step 440 is thenperformed. In step 440, exhaust flow sensor 285 of FIGS. 2 and 8 ispolled to determine if the flow is higher than a specified minimum flow.This is a check that the amount of air flow is sufficient to ensure noescape of gas from the cabinet into the room. If the flow is below aminimum flow then in step 445, PLC 345 initiates an exhaust flow alarmand no further action is taken automatically; otherwise the sub-routineof FIG. 9C is initiated through connector “A.”

Exhaust flow does not exert any control over the damper (e.g., damper145 of FIG. 3). That is, no control signals are sent to damper by PLC345 of FIG. 8 in response to exhaust flow sensor signals and theposition of damper is not affected by exhaust flow volume or changes inexhaust flow volume.

FIG. 9B describes the control logic for maintenance operation of the gascabinet. In step 450, PLC 345 of FIG. 8 receives a request formaintenance access to cabinet 100 via window 160 or door 135 (see FIG.1). In step 455, exhaust fans 260A and 260B of FIG. 2 are ramped up tothe corresponding pressure and flow rate for the maintenance position ofthe damper by control signals sent by PLC 345 to VFDs 275 of FIG. 2.Next, in step 460, exhaust static pressure sensor 280 of FIGS. 2 and 8is polled to determine if the pressure is lower than a specified maximumpressure. This is a check that the cabinet is at a negative pressurecompared to the ambient air pressure outside the cabinet. If thepressure is above the maximum pressure then in step 465, PLC 345 of FIG.8 initiates an exhaust pressure alarm and no further action is takenautomatically. If in step 460, the pressure is lower than the specifiedmaximum pressure, step 470 is performed. In step 470, the damper (e.g.,damper 145 of FIG. 3) is set to the maintenance position (e.g., an openposition) by control signals sent to the actuator (e.g., actuator 155 ofFIG. 3) and step 475 is then performed. In step 475, exhaust flow sensor285 of FIGS. 2 and 8 is polled to determine if the flow is higher than aspecified minimum flow. If the flow is below the minimum flow then instep 480, PLC 345 initiates an exhaust flow alarm and no further actionis taken automatically and no access is granted. If the flow is abovethe minimum flow then in step 485 PLC 345 of FIG. 8 unlatches door 135or window 160 of FIG. 1. Next, the sub-routine of FIG. 9C is initiatedthrough connector “A.”

FIG. 9C describes the control logic for an exhaust monitoringsub-routine. In step 490, exhaust flow sensor 285 of FIGS. 2 and 8 ispolled to determine if the flow is higher than a specified minimum flow.If the flow is higher than the minimum flow then the loop 490 and 495 isrepeated. If in step 490, the flow is lower than the minimum flow thenin step 500, high pressure isolation valve 225, low pressure valveisolation valve 240, and pneumatic cylinder valve 210 of FIGS. 1 and 8are closed by a control signals sent by PLC 345 to those valves (if notalready closed) and PLC 345 of FIG. 8 initiates an exhaust flow alarm.

FIG. 10 is a schematic block diagram of an exemplary programmable logiccontroller. In FIG. 10, a general purpose computer system 600 is used asprogrammable logic controller 310 (see FIG. 5), but alternatively, apurpose built logic controller may be used which would have similarcomponents to computer 600. In FIG. 10, computer system 600 has at leastone microprocessor or central processing unit (CPU) 605. CPU 605 isinterconnected via a system bus 610 to a random access memory (RAM) 615,a read-only memory (ROM) 620, an input/output (I/O) adapter 625 forconnecting a removable data and/or program storage device 630 and a massdata and/or program storage device 635, a user interface adapter 640 forconnecting a keyboard 645 and a mouse 650, a port adapter 655 forconnecting a data port 660 and a display adapter 665 for connecting adisplay device 670.

ROM 620 contains the basic operating system for computer system 600. Theoperating system may alternatively reside in RAM 615 or elsewhere as isknown in the art. Examples of removable data and/or program storagedevice 630 include magnetic media such as floppy drives and tape drivesand optical media such as CD ROM drives. Examples of mass data and/orprogram storage device 635 include electronic, magnetic, optical,electromagnetic, infrared, and semiconductor devices. Examples of acomputer-readable medium include a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk and an opticaldisk. Current examples of optical disks include compact disk-read onlymemory (CD-ROM), compact disk-read/write (CD-R/W) and DVD. In additionto keyboard 645 and mouse 650, other user input devices such astrackballs, writing tablets, pressure pads, microphones, light pens andposition-sensing screen displays may be connected to user interface 640.Examples of display devices include cathode-ray tubes (CRT) and liquidcrystal displays (LCD).

A computer program with an appropriate application interface may becreated by one of skill in the art and stored on the system or a dataand/or program storage device to simplify the practicing of thisinvention. In operation, information for the computer program created torun the present invention is loaded on the appropriate removable dataand/or program storage device 630, fed through data port 660 or typed inusing keyboard 645.

Generally, the method described herein with respect to the flow diagramsof FIGS.9A, 9B and 9C may be coded as a set of instructions on removableor hard media for use by programmable logic controller 310 (see FIG. 5)or general-purpose computer 600 (see FIG. 10) and stored as code 675 onRAM 615.

Thus the embodiments of the present invention provide a compressed gascylinder cabinet with regulated exhaust control and a method ofregulating exhaust of a compressed gas cylinder cabinet that is energyefficient.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A gas cabinet, comprising: an enclosure; a damperhaving at least two flow rate positions; an exhaust outlet; a set ofsensors; and a programmable logic controller configured to change a flowrate position of said damper from a first flow rate position to a secondflow rate position based on the state of said sensors.
 2. The gascabinet of claim 1, wherein said set of sensors includes one or moresensors selected comprising a gas flow sensor, a gas sensor, a gascylinder weight sensor, a low pressure sensor, or a high pressuresensor.
 3. The gas cabinet of claim 1, wherein said programmable logiccontroller is configured to change said damper from said first flow rateposition to said second flow rate position if one or more sensors ofsaid set of sensors indicates a gas leak within said enclosure, saidsecond flow rate position having a higher flow rate than said first flowrate position.
 4. The gas cabinet of claim 3, wherein (i) said firstflow rate position is a fully closed position and said second flowposition is a fully open position or (ii) said first flow rate positionis a partially closed position and said second flow rate position is amore open position than said first position.
 5. The gas cabinet of claim1, wherein said damper includes: a first set of fixed openings; amoveable plate having a second set of openings; means for moving saidsecond plate relative to said first set of openings; and wherein in afirst position of said plate corresponding to said first flow rateposition, said plate blocks each of said fixed openings and in a secondposition of said plate corresponding to said second flow rate position,each opening of said second set of openings aligns with a respectiveopening of said fixed openings.
 6. The gas cabinet of claim 1, whereinsaid damper includes: a first set of fixed openings; a moveable platehaving a second set of openings; means for moving said second platerelative to said first set of openings; and wherein in a first positionof said plate corresponding to said first flow rate position, said plateblocks more of each opening of said fixed openings then are blocked bysaid plate in a second position corresponding to said second flow rateposition.
 7. The gas cabinet of claim 1, wherein said damper includes: aset of moveable louvers and means for opening and closing said louvers.8. The gas cabinet of claim 1, further including: a set of valvesconfigured to control a flow of gas from a gas cylinder mounted in saidcabinet to a gas supply line exiting from said cabinet; and wherein saidprogrammable logic controller is configured to close said set of valvesif one or more sensors of said set of sensors indicates an out ofspecification condition.
 9. The gas cabinet of claim 8, wherein saidexhaust outlet is connected to an exhaust fan through an exhaust ductand said programmable logic controller is connected to an exhaust staticpressure sensor in said exhaust duct; and said programmable logiccontroller is configured to (i) increase the fan speed of said exhaustfan if one or more sensors of said set of sensors indicates a gas leakand (ii) not change the flow rate position of said damper if saidexhaust static pressure sensor indicates that the pressure in saidexhaust duct is greater than a preset minimum pressure.
 10. The gascabinet of claim 8, wherein said exhaust outlet is connected to anexhaust fan through an exhaust duct and said programmable logiccontroller is connected to an exhaust flow sensor in said exhaust duct;and said programmable logic controller is configured to (i) increase thefan speed of said exhaust fan if one or more sensors of said set ofsensors indicates a gas leak and (ii) to close said set of valves ifsaid exhaust flow sensor indicates that the air flow rate is less than apreset minimum flow rate.
 11. The gas cabinet of claim 1, wherein saidenclosure is fitted with a door.
 12. The gas cabinet of claim 11,wherein said damper is the only means for air entry into said cabinetwhen said door is closed and latched.
 13. The gas cabinet of claim 11,wherein said damper is contained with said door.
 14. A method,comprising: providing a gas cabinet, comprising: an enclosure; a damperhaving at least two flow rate positions; an exhaust outlet; a set ofsensors; and a programmable logic controller configured to change theflow rate position of said damper from a first flow rate position to asecond flow rate position based on the state of said sensors; and if theexhaust static pressure within said cabinet is lower than a presetminimum pressure then changing said damper from said first flow rateposition to said second flow rate position if one or more sensors ofsaid set of sensors indicates a gas leak within said enclosure, saidsecond flow rate position having a higher flow rate than said first flowrate position.
 15. The method of claim 14, wherein (i) said first flowrate position is a fully closed position and said second flow rateposition is a fully open position or (ii) said first flow rate positionis a partially closed position and said second flow rate position is amore open position than said first position.
 16. The method of claim 14,said gas cabinet further including: a set of valves configured tocontrol a flow of gas from a gas cylinder mounted in said cabinet to agas supply line exiting from said cabinet; and closing said set ofvalves if one or more sensors of said set of sensors indicates an out ofspecification condition.
 17. The method of claim 16, wherein saidexhaust outlet is connected to an exhaust fan through an exhaust ductand said programmable logic controller is connected to an exhaust staticpressure sensor in said exhaust duct; increasing the fan speed of saidexhaust fan if one or more sensors of said set of sensors indicates agas leak; and not changing said flow rate position of said damper ifsaid exhaust static pressure sensor indicates that the pressure in saidexhaust duct is greater than said preset minimum pressure.
 18. Themethod of claim 16, wherein said exhaust outlet is connected to anexhaust fan through an exhaust duct and said programmable logiccontroller is connected to an exhaust flow sensor in said exhaust duct;increasing the fan speed of said exhaust fan if one or more sensors ofsaid set of sensors indicates a gas leak; and closing said set of valvesif said exhaust flow sensor indicates that the air flow rate is lessthan a preset minimum flow rate.
 19. The method of claim 14, whereinsaid set of sensors includes one or more sensors selected from the groupconsisting of a gas flow sensor, a gas sensor, a gas cylinder weightsensor, a low pressure sensor, and a high pressure sensor.
 20. Themethod of claim 14, wherein said damper includes a first set of fixedopenings and a moveable plate having a second set of openings; andchanging said damper from a first position corresponding to said firstflow rate position to a second position corresponding to said secondflow rate position includes moving said moveable plate relative to saidfirst set of openings wherein in said first position, said plate blocksmore of each opening if said fixed openings then are blocked by saidplate in a second flow rate position.
 21. The method of claim 14,wherein said damper includes a first set of fixed openings and amoveable plate having a second set of openings; and changing said damperfrom a first position corresponding to said first flow rate position toa second position corresponding to said second flow rate positionincludes moving said moveable plate relative to said first set ofopenings wherein in said first position said plate, said plate blockseach of said fixed openings and in said second position of said plateeach opening of said second set of openings align with respectiveopenings of said fixed openings.
 22. The method of claim 14, furtherincluding: monitoring the state of said sensors and if said sensorsindicate a gas leak, first increasing the speed of exhaust fansconnected to said exhaust outlet followed by closing gas delivery valveswithin said cabinet followed by determining if an exhaust pressure ofsaid cabinet is less than a preset minimum pressure; and performing saidchanging said damper from said first flow rate position to said secondflow rate position only if said exhaust pressure is less than saidpreset minimum pressure.
 23. The method of claim 22, further including:determining if an exhaust flow rate of said cabinet is greater than apreset exhaust flow rate and if said exhaust flow rate of said cabinetis not greater than a preset exhaust flow rate then closing said gasdelivery valves if said gas delivery valves are not already closed. 24.The gas cabinet of claim 14, wherein said enclosure is fitted with adoor.
 25. The gas cabinet of claim 24, wherein said damper is the onlymeans for air entry into said cabinet when said door is closed andlatched.
 26. The gas cabinet of claim 24, wherein said damper iscontained with said door.